The apparatus is from LaParola, but it seems to have skipped Sinaiticus and Vaticanus in one spot, and I have put them back, marked with a tilde (~).
1.
1.18
Κηφᾶν] p46 p51 א* A B 33 424c 467 823 920 1739 1912 syrp syrh(mg) syrpal copsa copbo eth WH NR CEI Riv Nv NM
Πέτρον] אc D F G K L P Byz ς ND Dio TILC
I select Cephas here because (A) our earliest (p46) and often most reliable (א B) extant manuscripts have Cephas and (B) I cannot think of a good reason to have turned Peter into Cephas here.
Marcion may have lacked this entire section, verses 18-24, however, so the choice here may not matter so much.
2.
2.9
Ἰάκωβος καὶ Κηφᾶς καὶ Ἰωάννης] ~א ~B Byz ς WH
Ἰάκωβος καὶ Πέτρος καὶ Ἰωάννης] p46 itr
Πέτρος καὶ Ἰάκωβος καὶ Ἰωάννης] D F G itd itg goth Marcion Origenlat Ambrosiaster Victorinus-Rome Ephraem Marius Mercator
In verses 7-8 I have Peter, because I am not aware of any variants for these two instances. But I also take the part highlighted in yellow as an interpolation; this has been suggested before for many reasons, not least the weirdness of Paul switching back and forth between Cephas and Peter as names for the same man for no particular reason. The very lack of manuscript variations for the name of Peter in these two verses may point to this part having been added later than the other verses about Peter/Cephas, all of which contain such variants; the interpolation simply postdates the textual wars which produced those variants.
3.
2.11
Κηφᾶς] א A B C H P 33 103 104 181 263 424c 436 vg syrp syrh(mg) copsa copbo arm eth WH NR CEI Riv Nv NM
Πέτρος] D F G K L Byz syrh(text) goth Marcion Victorinus-Rome Chrysostom Marius Mercator ς ND Dio TILC
2.14
Κηφᾷ] p46 א A B C H 10 33 88 255 263 424c 467 1319 2127 vg syrp copsa copbo arm eth WH NR CEI Riv Nv NM
Πέτρῳ] D F G K L P Byz itd itg vgmss syrh goth ς ND Dio TILC
These two instances have to go together in the text, for surely Paul is rebuking the same man he is opposing in Antioch. But here is where I am differing from the usual textual reconstructions in selecting Peter instead of Cephas. My reason is simply that Cephas seems to be the Alexandrian (א B) or Egyptian (p46) favorite for these verses, and we can be fairly certain that a debate over Cephas and Peter in this very context took place in Alexandria:
This is Clement of Alexandria, of course. So the situation in 2.11, 14 is very much unlike the situation in 1.18, since here there is a clear and obvious reason why Peter might have been changed to Cephas: to spare him the wrath of the apostle Paul and pawn it off on the seemingly less important Cephas.
If this reconstruction is correct, then Paul went to visit Cephas (1.18, assuming for the sake of argument that this is part of the original text) in Jerusalem, and then went again to visit the three pillars: James, Cephas, and John. Later, however, in Antioch, he had a run-in with a different person, named Peter. If 1.18 is original, then both Cephas and Peter are known enough to the Galatians (at least) that they do not require a special introduction beyond their name alone (1.18; 2.11); if 1.18 is not, then Cephas is not necessarily that well known, as he is given a more proper introduction as one of the "pillars" in 2.9.
Again, I have no absolute commitment to this scenario; just throwing it out there, as it occurred to me recently and differs from the usual textual reconstructions. What do you think?
Ben.
ETA: Parking this here for future reference:
10 The witnesses herein: Attarmalki son of Kilkilan; Sinkishir son of Shabbethai; Saharakab son of Cepha [בר כפא];
11 Nabushillen son of Bethelrai; Eshemram son of Eshemshezib; Varyazata son of Bethelzabad;
12 Heremnathan son of Paho; Eshemzabad son of Shawyan.
The papyrus in question is dated to around 416 BC. It is also known as BMAP #8, from the Brooklyn Museum Aramaic Papyri.